The invention discloses a floating body type overhauling steel sluice gate with an adjustable orifice width. A sluice-gate gate leaf of the floating body type overhauling steel sluice gate with the adjustable orifice width consists of an intermediate-section sluice-gate gate leaf, and a left-section sluice-gate gate leaf and a right-section sluice-gate gate leaf which are symmetrically connected to two ends of the intermediate-section sluice-gate gate leaf in a lapping manner; the left-section sluice-gate gate leaf and the right-section sluice-gate gate leaf are the same in structure and are symmetrically arranged; the intermediate-section sluice-gate gate leaf consists of a box-shaped sealing cavity at a middle part and opening adjusting cavities at two ends; sealing box-shaped lapping units of the left-section sluice-gate gate leaf and the right-section sluice-gate gate leaf are connected into the opening adjusting cavities of the intermediate-section sluice-gate gate leaf through sliding rails and sliding ways in an insertion manner; a sluice gate orifice width regulating device is arranged between each of the left-section sluice-gate gate leaf and the right-section sluice-gate gate leaf, and the intermediate-section sluice-gate gate leaf. When the floating body type overhauling steel sluice gate with the adjustable orifice width is designed, stress calculation is carried out according to the maximum width of a sluice gate needing to be overhauled; structural arrangement is carried out according to the maximum width and the minimum width of the sluice gate; the lapping lengths of the left section and the right section on the intermediate section and the number of lapping units are determined according to the height dimension and the thickness dimension of the sluice gate; optimization design is carried out by combining the stress calculation with the structural arrangement, and the stress of the sluice gate is enabled to meet relevant code requirements, and moreover, to meet structural and constructional requirements.